Questions about Nintendo Pokémon Tekken DX

It doesn't matter in my opinion. The indication DE (or German) is only for the packaging. When you first start the game you can choose in what language you want to play the game.

No, all the pokemons available in the version are unlocked, then there is the possibility to add more with the purchase of DLC Exagide - pack n°1 Tortank - pack n°2